JP7493347B2 - Heat-expandable and heat-curable adhesive sheet - Google Patents

Description

One aspect of the present disclosure relates to a thermally expandable and thermosetting adhesive sheet.

Conventionally, there is an adhesive sheet described in Patent Document 1. This adhesive sheet is a thermally expandable adhesive sheet that includes a base material, two thermally expandable adhesive parts provided on both sides of the base material, and two adhesive permeable layers provided on the surface of each of the two adhesive parts and through which the adhesive can permeate when the adhesive thermally expands. By heating the adhesive sheet, the adhesive sheet can be expanded and at the same time the adhesive can be made to appear on the outermost surface of the adhesive sheet.

JP 2019-203062 A

Here, the above-mentioned adhesive sheet has nonwoven fabric as an adhesive permeable layer on both sides of the substrate. In this case, the nonwoven fabric is subject to restrictions in terms of thickness and density. For example, if the nonwoven fabric is too thin, the adhesive will easily seep out, resulting in problems such as reduced manufacturing stability and storage stability. If the density of the nonwoven fabric is too low, there is a similar problem. If the nonwoven fabric is too thick, there is a problem that the adhesive will not seep out properly. If the density of the nonwoven fabric is too high, there is a similar problem. Therefore, the adhesive sheet needs to have nonwoven fabric set to a specified range of thickness and density. In this case, there is a problem that the degree of freedom in designing the adhesive sheet is reduced.

The adhesive sheet according to one embodiment of the present disclosure is a thermally expandable and thermally curable adhesive sheet, comprising a substrate and a first layer provided on at least one surface of the substrate, the first layer comprising an adhesive portion having thermally expandable first particles and second particles of a different material than the first particles, the second particles being larger than the first particles.

According to one embodiment of the present disclosure, an adhesive sheet that can improve design freedom can be provided.

FIG. 2 is a cross-sectional view showing a state before thermal expansion of an adhesive sheet according to an embodiment of the present disclosure. 2 is a cross-sectional view showing a state after thermal expansion of the adhesive sheet shown in FIG. 1. 6 is a photograph of the surface of the adhesive part of Comparative Example 1 and Example 1. 1 is a table showing experimental conditions and experimental results.

Below, the embodiments for implementing the present disclosure will be described in detail with reference to the attached drawings. In the description of the drawings, the same or equivalent elements are given the same reference numerals, and duplicate descriptions will be omitted.

An embodiment of the present invention will be described in detail. Below, an example in which an adhesive sheet is applied to a motor will be described. The stator body of the motor has a cylindrical shape and has multiple slots along the inner circumference of the cylinder. A coil for the motor is disposed in the slot. In general, the stator body and the coil are bonded to each other and are electrically insulated from each other.

Conventionally, an insulator is sandwiched between the stator body and the coil, and then a liquid adhesive is allowed to penetrate into the gap to bond and secure the various components. An adhesive sheet is placed between the motor's stator body and coil, which are the bonded components, and the adhesive strength of the adhesive sheet bonds the two bonded components together. A specified gap is provided between the bonding surfaces of the two bonded components, and an adhesive sheet is placed in that gap.

When bonding the stator body and the coil, first prepare an adhesive sheet in a state before it exerts its adhesive force, i.e., in a tack-free state, and place the adhesive sheet between the bonding surfaces of the bonded members. At this time, it is preferable that the thickness of the adhesive sheet is slightly narrower than the gap between the bonded members. After placing the adhesive sheet in the specified position, the adhesive sheet is heated, causing the adhesive sheet to transition from a tack-free state to a state in which it has adhesive force on its surface.

Figure 1 is a cross-sectional view showing the structure of an adhesive sheet. More specifically, Figure 1 is a cross-sectional view of an adhesive sheet before the adhesive sheet exerts its adhesive force, i.e., in a tack-free state. As shown in Figure 1, the adhesive sheet 1 in a tack-free state comprises a plate-shaped substrate 3, a first layer 4, and a second layer 6. The first layer 4 is provided on one main surface 3a of the substrate 3. The second layer 6 is provided on the other main surface 3b of the substrate 3. The first layer 4 comprises an adhesive portion 11 and second particles 12. The second layer 6 comprises an adhesive portion 13 and an adhesive permeable layer 14.

The substrate 3 is a base for forming the adhesive parts 11 and 13, and is a member that essentially determines the size of the adhesive surface of the adhesive sheet 1. As the substrate 3, for example, a polyethylene naphthalate (PEN) film may be used in consideration of strength, heat resistance, insulation, etc. However, since it is sufficient to function as a base for forming the adhesive parts 11 and 13 during the manufacturing stage of the adhesive sheet 1, any material may be used as long as it has enough strength to support the adhesive parts 11 and 13 and does not reduce the adhesive force of the adhesive that constitutes the adhesive parts 11 and 13 when heated. The thickness of the substrate 3 may be adjusted in consideration of the gap of the adherend. In other words, in addition to the role of adhering the stator body and coil of the motor, which are the adherends, the adhesive sheet 1 also plays a role of creating a gap between the adherends, so if the gap is large, the thickness of the substrate 3 can be increased to suitably fill the gap.

The adhesive portion 11 of the first layer 4 is a layer of a thermally expandable adhesive formed on one of the main surfaces 3a of the substrate 3. The thickness of the adhesive portion 11 is set to 10 μm or more and 300 μm or less. The adhesive portion 11 has an adhesive composition 21 and first particles 22. In this specification, a pressure sensitive adhesive is also a type of adhesive.

As the adhesive composition 21, a composition that is almost solid at room temperature, becomes fluid when heated, and hardens when cooled can be used. As such an adhesive composition 21, a thermosetting epoxy adhesive composition can be used.

Epoxy resins contained in the thermosetting epoxy adhesive composition include those obtained from epoxy compounds (monomer epoxy compounds or polymer epoxy compounds) having at least one oxirane ring that can be polymerized by a ring-opening reaction. The epoxy compounds may be aliphatic, alicyclic, aromatic, or heterocyclic. Bisphenol epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin, epoxy resins having an aliphatic skeleton such as hexanediol diglycidyl ether, glycidylamine type epoxy resins such as triglycidylaminophenol, novolac epoxy resins such as phenol novolac epoxy resin and cresol novolac epoxy resin, brominated epoxy resins, alicyclic epoxy resins, and mixtures thereof can be used, but are not limited to these.

As the curing agent or curing accelerator contained in the thermosetting epoxy adhesive composition, various heat curing agents known in the art to be usable as a heat curing agent for epoxy resins can be used. Examples of heat curing agents include compounds that react with the oxirane ring of the epoxide to substantially crosslink the epoxide to form a crosslinked polymer network. These compounds contain at least one nucleophilic or electrophilic moiety (e.g., an active hydrogen atom) that causes a crosslinking reaction. As will be understood by those skilled in the art, heat curing agents and curing accelerators are often not distinguished from each other. There is no particular limitation on the curing agent as long as it can cure the epoxy resin with heat, but it is preferable to use a latent curing agent that is inactive near room temperature and activated by heat. Examples of latent curing agents include dicyandiamide and its derivatives, hydrazide compounds, boron trifluoride-amine complexes, and reaction products of amine compounds with isocyanate compounds or urea compounds (urea derivatives). A latent curing accelerator may be used in combination with the curing agent for the epoxy resin. Examples of curing accelerators include imidazole compounds, reaction products of amine compounds and epoxy compounds (amine-epoxy adducts), urea derivatives, etc.

If desired, the adhesive composition may further contain additional components such as a thermoplastic resin (such as a phenoxy resin (a polyhydroxy polyether synthesized from bisphenols and epichlorohydrin)), a toughening agent (such as a core-shell agent), a rheological agent (such as nanosilica particles), a silane coupling agent, a flame retardant, an impact modifier, a heat stabilizer, a processing aid, a lubricant, a reinforcing agent, a colorant, a photopolymerization initiator, a crosslinking agent, a chain transfer agent, etc. As each of these additional components, various agents conventionally known in the art can be used.

The first particles 22 are thermally expandable particles contained in the adhesive composition 21. The first particles 22 are present in the adhesive composition 21 in a substantially uniformly mixed state. The first particles 22 thermally expand when heated. The thermal expansion of the first particles 22 increases the volume of the entire adhesive portion 11 (see FIG. 2). The particle diameter of the first particles 22 may be smaller than 50 μm, and may further be smaller than 40 μm. The particle diameter is determined by a laser diffraction type particle size distribution measuring device. Examples of the material of the first particles 22 include those having a capsule structure in which a thermoplastic resin such as vinylidene chloride polymer, acrylonitrile copolymer, or acrylic polymer is used as an outer shell and isobutane or isopentane is enclosed inside as a foaming agent.

The second particles 12 of the first layer 4 are arranged in the adhesive portion 11 and are particles made of a different material from the first particles 22. A part of the second particles 12 protrudes from the surface 11a of the adhesive portion 11 before the adhesive portion 11 thermally expands (the state shown in FIG. 1). As a result, the second particles 12 function as a member that separates the surface 11a of the adhesive portion 11 from the bonded member. Also, when the adhesive portion 11 thermally expands, the adhesive composition 21 overflows from the gaps between the multiple second particles 12. As a result, the second particles 12 allow the surface 11a of the adhesive portion 11 to be exposed to the bonded member (the state shown in FIG. 2). Specifically, the thickness of the adhesive portion 11 is "t", and the distance between the outer end (the most protruding part) of the second particles 12 and the main surface 3a of the substrate 3 is "L". In this case, the relationship "L>t" holds. At this time, the amount of protrusion of the second particles 12 is "Rz (=L-t)". The amount of protrusion Rz may be greater than 6 μm and less than 60 μm. In the following explanation, unless otherwise specified, the explanation is given for the state before the adhesive portion 11 thermally expands (the state shown in FIG. 1).

The second particles 12 are larger than the first particles 22. This makes it easier for the second particles 12 to protrude from the surface 11a of the adhesive portion 11. Specifically, the particle size of the second particles 12 may be greater than 10% of the particle size of the first particles 22, or even greater than 400%. The particle size of the second particles 12 may be greater than 10 μm, or even greater than 20 μm. The second particles 12 may also be greater than the thickness of the adhesive portion 11. That is, the particle size of the second particles 12 may be greater than the thickness of the adhesive portion 11. In this case, even if the second particles 12 are arranged in close proximity to the main surface 3a of the substrate 3 (see, for example, the second particles 12A), the second particles 12 protrude from the surface 11a of the adhesive portion 11. However, the second particles 12 may be less than the thickness of the adhesive portion 11. Since the second particles 12 may be arranged at a position separated from the main surface 3a of the base material 3 (see, for example, second particle 12B), the second particles 12 can protrude from the adhesive portion 11 regardless of their size. The upper limit of the particle size of the second particles 12 is not particularly limited, but is set to a size within a range in which the surface 11a of the adhesive portion 11 can be exposed to the adherend when the adhesive portion 11 thermally expands.

The second particles 12 may have a spherical shape. The shape of the second particles 12 is not particularly limited, and may be a polyhedral shape. However, when the second particles 12 have a flat shape, depending on the orientation of the second particles 12 in the adhesive part 11, the second particles 12 may not protrude from the surface 11a, or the amount of protrusion may be small. Therefore, it is preferable that the second particles 12 have a shape that has little change in dimension depending on the measurement direction. Specifically, it is preferable that the value (long axis dimension) when measured from the direction in which the dimension of the second particles 12 is the largest is within a range of 200% or less of the value (short axis dimension) when measured from the direction in which the dimension is the smallest. The particle size of the second particles 12 is determined by the dimension of the short axis.

The second particles 12 may be formed of a heat-resistant material. The second particles 12 may be formed of a material having a lower thermal expansion than at least the first particles 22. The second particles 12 may be formed of an organic material or an inorganic material. Specifically, materials such as cross-linked (meth)acrylic acid ester copolymer, cross-linked polystyrene, cross-linked urethane, cross-linked silicone, and nylon are used as organic materials. Materials such as silica, aluminum hydroxide, magnesium hydroxide, aluminum oxide, magnesium oxide, titanium oxide, and zirconium oxide are used as inorganic materials.

The adhesive portion 13 of the second layer 6 has the same configuration as the adhesive portion 11 of the first layer 4.

When the first particles 22 of the adhesive portion 13 expand, the adhesive permeable layer 14 of the second layer 6 allows the adhesive composition 21 to penetrate from one main surface side to the other main surface side of the adhesive permeable layer 14. More specifically, the adhesive permeable layer 14 has a structure having at least a plurality of holes penetrating from one main surface to the other main surface. By making the adhesive permeable layer 14 have a structure having a plurality of holes, when the adhesive composition 21, which is in contact with only one main surface of the adhesive permeable layer 14 before heating, expands, the adhesive composition 21 can reach the other main surface of the adhesive permeable layer 14 through the holes. In addition, as a material constituting the adhesive permeable layer 14, a material having a glass transition temperature higher than the curing start temperature of the adhesive composition 21 is selected. Specifically, a material that can be used as the adhesive permeable layer 14 can be a nonwoven fabric based on natural fibers, chemical fibers, or a mixture thereof, and a representative example is a cellulose-based nonwoven fabric. Such nonwoven fabrics have many through holes inside, so that the adhesive composition 21 in contact with one main surface can pass through the inside of the nonwoven fabric and reach the other main surface under certain conditions.

The nonwoven fabric preferably has a basis weight of at least 10 g/m ² , preferably 11 g/m ² or more. This is because, as a result of experiments by the inventors, if the basis weight of the nonwoven fabric is too small, sufficient adhesive strength cannot be obtained after the adhesive composition 21 is cured. Also, if the basis weight of the nonwoven fabric is too small, the adhesive composition 21 will seep out of the nonwoven fabric during the adhesive sheet production process, causing a problem of blocking during storage in a rolled state. Also, it is preferable that the nonwoven fabric has a thickness of 50 μm or less, preferably 47 μm or less. This is because, as a result of experiments by the inventors, if the thickness of the nonwoven fabric is too large, the amount of adhesive material seeping out to the surface of the nonwoven fabric when the adhesive sheet is heated will be reduced, and the shear adhesive strength of the adhesive sheet 1 will decrease.

When using the adhesive sheet 1, the adhesive sheet 1 in a tack-free state is placed between the adhesive surfaces of components that are placed with a specified gap between them. At this time, because the adhesive sheet 1 is in a tack-free state, it is possible to prevent the adhesive sheet 1 from unintentionally sticking to the components, and the adhesive sheet 1 can be easily placed even when the gap between the adherend components is relatively narrow. After placing the adhesive sheet 1 in a fixed position between the adherend components, the adhesive sheet 1 is heated, whereby the adhesive sheet 1 transitions from a tack-free state to a state in which the surface has adhesive force.

Figure 2 is a cross-sectional view showing the structure of the adhesive sheet. More specifically, Figure 2 is a cross-sectional view of the adhesive sheet when the adhesive sheet is exerting its adhesive force.

In the state shown in FIG. 2, the layer structure of the adhesive sheet 1 is different from the layer structure of the adhesive sheet 1 in the tack-free state. In the state shown in FIG. 2, unlike the state shown in FIG. 1, second particles 12 are embedded inside the adhesive portion 11 provided on one main surface 3a of the substrate 3. Also, an adhesive permeable layer 14 is embedded inside the adhesive portion 13 provided on the other main surface 3b of the substrate 3. This provides adhesive force on both sides of the adhesive sheet 1.

When the adhesive sheet 1 in a tack-free state is heated, the adhesive portions 11 and 13 expand. As a result, the second particles 12 on the surface 11a of the adhesive portion 11 are pressed against the adhesive surface of the adherend. Further expansion of the adhesive portion 11 causes the adhesive composition 21 to overflow from the gaps between the second particles 12. The phenomenon of the adhesive composition 21 seeping out onto the outer surface of the gaps between the second particles 12 occurs on one main surface of the adhesive sheet 1. Meanwhile, the adhesive permeable layer 14 on the surface of the adhesive portion 13 is pressed against the adhesive surface of the adherend. Further expansion of the adhesive portion 13 causes the adhesive composition 21 to enter the adhesive permeable layer 14 and seep out onto the outer surface of the adhesive permeable layer 14. The phenomenon of the adhesive composition 21 seeping out onto the outer surface of the adhesive permeable layer 14 occurs on the other main surface of the adhesive sheet 1.

Therefore, when the adhesive sheet 1 in the tack-free state shown in FIG. 2 is heated, the adhesive composition 21 above the substrate 3 penetrates the gaps between the second particles 12 above the substrate 3 and appears on the upper surface of the adhesive sheet 1. As a result, the adhesive composition 21 is interposed between the second particles 12 and the adhesive surface of the adherend, and the second particles 12 are substantially buried inside the adhesive portion 11. Also, the adhesive composition 21 below the substrate 3 penetrates the adhesive permeable layer 14 below the substrate 3 and appears on the lower surface of the adhesive sheet 1. As a result, the adhesive composition 21 is interposed between the adhesive permeable layer 14 and the adhesive surface of the adherend, and the adhesive permeable layer 14 is substantially buried inside the adhesive portion 13. In the state shown in FIG. 2, the adhesive composition 21 is present on the outermost surface of the adhesive sheet 1, so that the adhesive sheet 1 exerts its adhesive force. Then, by curing the adhesive composition 21, the adherend members can be bonded to each other by the adhesive sheet 1. In addition, when the adhesive sheet 1 is heated to expand the adhesive composition 21, the second particles 12 and the adhesive permeable layer 14 are embedded in the adhesive portions 11 and 13 and left in the adhesive portions 11 and 13, so that the second particles 12 and the adhesive permeable layer 14 function as members that suppress the spread of the adhesive composition 21 in the planar direction.

In this way, by transitioning the adhesive sheet 1 from a tack-free state to a state in which both sides have adhesive force, the adhesive sheet 1 can be easily positioned in a predetermined position. In addition, by expanding the adhesive sheet 1 to make it conformable to the surface shape of the adhesive surface, the gaps between the adherends can be filled, and even if there is a processing tolerance on the surface of the adhesive surface, the adherends can be bonded together appropriately regardless of the tolerance.

The adhesive sheet 1 can also be used in a folded state according to the shape of the gap in the adherend.

In view of the above, the adhesive sheet is a thermally expandable and thermally curable adhesive sheet comprising a substrate and a first layer provided on at least one surface of the substrate, the first layer comprising an adhesive portion having an adhesive composition and thermally expandable first particles contained in the adhesive composition, and second particles disposed in the adhesive portion and made of a different material than the first particles, the second particles being larger than the first particles.

In this adhesive sheet, the first layer is arranged in the adhesive portion and includes second particles of a material different from the first particles. The second particles are larger than the first particles. Therefore, a part of the second particles can protrude from the surface of the adhesive portion. Before thermal expansion, the protruding parts of the second particles can separate the surface of the adhesive portion from the adherend. On the other hand, when the adhesive portion is thermally expanded, the adhesive portion overflows from the gaps between the second particles. This makes it possible for the adhesive portion to adhere to the adherend. Unlike a configuration in which an adhesive permeable layer is provided on the adhesive portion, the first layer has a configuration in which the second particles are arranged in the adhesive portion. Therefore, the second particles have less effect on the thickness of the first layer, etc., compared to the adhesive permeable layer. Therefore, the degree of freedom in designing the adhesive sheet can be improved.

The adhesive sheet may include the above-mentioned first layer on at least one surface of the substrate, and the configuration of the other surface is not particularly limited. For example, the adhesive sheet may have no adhesive portion on the other surface of the substrate, and the surface of the substrate may be exposed. Alternatively, the adhesive sheet may have the first layer on both surfaces of the substrate.

The second particles may be larger than the thickness of the adhesive portion. In this case, the second particles can protrude from the surface of the adhesive portion regardless of the position of the second particles in the adhesive portion.

The second particles may have a spherical shape. In this case, the second particles can protrude from the surface of the adhesive portion regardless of the orientation of the second particles in the adhesive portion.

The second particles may be made of a heat-resistant material. In this case, damage to the second particles caused by heating due to thermal expansion can be suppressed.

The first layer is provided on one side of the substrate, and the second layer is provided on the other side of the substrate, and the second layer is provided on the surface of the adhesive portion, and the second layer may include an adhesive portion and an adhesive permeable layer provided on the surface of the adhesive portion and through which the adhesive composition can permeate when the first particles are thermally expanded. In this case, the adhesive sheet has the second particles on one side and the adhesive permeable layer on the other side. For example, when the first layer and the first layer are brought into contact when the adhesive sheets are stacked and stored, there is a possibility that the adhesive portions of both layers will be bonded. On the other hand, when the first layer and the second layer are brought into contact, an adhesive permeable layer can be interposed between the adhesive portions. This can prevent the adhesive sheets from being bonded to each other during storage.

The adhesive permeable layer may be formed from a material whose glass transition temperature is higher than the curing initiation temperature of the adhesive composition that constitutes the adhesive portion. In this case, the adhesive permeable layer can be prevented from being affected by heating for curing the adhesive composition.

The adhesive permeable layer may be a nonwoven fabric.

The first layer may be provided on one side of the substrate, and a third layer having adhesiveness at 20°C may be provided on the other side of the substrate. The third layer includes an adhesive material having adhesiveness (with initial tack) at 20°C. When the third layer is provided, the third layer is bonded to the adherend, and the first layer is inserted between the adherend and another adherend while sliding the first layer, and then heated to expand and harden the first layer, thereby bonding the adherend and the other adherend. The third layer may be both adhesive at room temperature and thermosetting, and in this case, the third layer is also thermoset when heated, along with the expansion and thermosetting of the first layer, thereby increasing the bonding strength. The third layer may be exposed, and a liner may be provided on the outside.

The particle size of the first particles may be less than 50 μm.

The particle size of the second particles may be greater than 10 μm.

Next, we will describe in detail an embodiment of the present invention.

[Example 1]
NPPN442 (manufactured by NANYA) as an epoxy resin was softened in advance by heating in an oven at 65° C. In a 225 ml glass container, 48.5 g of the resin, 0.49 g of YSLV-80XY (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.) as an epoxy resin, and 35 g of methyl ethyl ketone (MEK) (manufactured by Wako Pure Chemical Industries, Ltd.) as a solvent were added, and all of the resin was dissolved in MEK. 3.5 grams of BTA-731 (manufactured by Dow Chemical Co.) as a toughening agent (core-shell toughener), 8.07 grams of DICYANEX1400F (manufactured by Evonik Japan Co., Ltd.) as a curing agent, 4.2 grams of nanosilica Ultrabond (manufactured by Cabot Japan Co., Ltd.) as a rheological agent, 14 grams of YP-50EK35 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.) as a thermoplastic resin, 0.28 grams of OFS-6040 (manufactured by Dow Corning Toray Co., Ltd.) as a silane coupling agent, 6 grams of FN-100SSD (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) as a first particle, and 0.65 grams of 2MZA-PW (manufactured by Shikoku Kasei Kogyo Co., Ltd.) as a curing accelerator were added to a glass container and dispersed using a homogenizer for about one hour to obtain an adhesive solution A.

15 grams of adhesive solution A prepared as described above was weighed into a 225 ml glass container. Then, 2 grams of SE-050T (second particles with an average particle size of 43 μm) (manufactured by Negami Chemical Industries) were added to the glass container and mixed with an automatic revolution mixer at 2000 rpm for 2 minutes to obtain a solution of adhesive solution A and second particles (which may be called adhesive solution B). This solution was applied to Teonex Q51 (manufactured by Toyobo Film Solutions Co., Ltd.) (75 μm PEN film) and dried to an adhesive coating weight of approximately 51 g/SQM. The coated liner was dried at 65°C for 3 minutes and then at 100°C for 3 minutes.

The adhesive solution A prepared as described above was applied to a silicone liner, Purex A50 (Teijin DuPont Films Japan), and dried to an adhesive coating weight of approximately 47 g/SQM. The coated liner was dried at 65°C for 3 minutes and then at 100°C for 3 minutes.

The adhesive sheet containing the second particles on the PEN film was laminated to a silicone liner, Purex A50. The adhesive surface was then brought into contact with the silicone coating. The silicone liner-covered adhesive sheet was then laminated to the PEN so that the adhesive surface was in contact with the uncoated surface of the PEN. A laminated sheet was formed by passing through a rubber roll heated at 60°C. The liner of the adhesive portion not containing the second particles was removed, and Daio 14 gram paper (manufactured by Daio Paper Co., Ltd.) was laminated to the adhesive portion, and the laminated sheet was laminated again by passing through a rubber roll heated at 60°C. Finally, the silicone liner of the adhesive portion not containing the second particles was removed, and an adhesive sheet was obtained.

The conditions of the adhesive sheet according to Example 1 are shown in the table of FIG. 3. Among the items in the table, "adhesive" refers to adhesive solution A in paragraph 0043 of Example 1, and is expressed in grams. The same adhesive as in Example 1 is used for the other examples. "SE050T" refers to the weight of SE050T, which is the second particle having an average particle size of 43 μm, and is expressed in grams. "SE030T" refers to the weight of SE030T, which is the second particle having an average particle size of 34 μm, and is expressed in grams. "J5P" refers to the weight of J5P, which is the second particle having an average particle size of 3.5 μm, and is expressed in grams. "MEK" refers to the amount of MEK further added to adhesive solution A, and is expressed in grams. "Volume fraction of second particles" refers to the approximate volume fraction of the second particles calculated assuming that the adhesive portion containing the first particles and the second particles have a specific gravity of 1.0. "Adhesive application amount" refers to the amount of adhesive applied to the first layer after drying. "Paper adhesive application amount" refers to the amount of adhesive applied to the second layer. "Total thickness" refers to the thickness of the entire adhesive sheet. "L" refers to the value of dimension L shown in Figure 1. "Rz" refers to the amount of protrusion Rz shown in Figure 1. "t" refers to the value of dimension t shown in Figure 1. "Blocking (against paper)" refers to the results of the blocking test described below. "Shear force" refers to the results of the shear force test described below.

[Examples 2 to 7]
This embodiment is the same as the first embodiment except that the conditions shown in the table of FIG. 3 were changed.

[Comparative Example]
A comparative example 1 was prepared that did not contain the second particles in the adhesive part. In addition, the comparative example 1 did not have paper as an adhesive permeable layer. A comparative example 2 was prepared that used J5P with second particles of 3.5 μm. In addition, a comparative example 3 was prepared that had paper on both sides and did not have the second particles in the adhesive part.

[Blocking test]
The sheets produced in the examples and comparative examples were subjected to a blocking test in the following manner.
・Sample size: 25mm x 25mm
- Two samples of the same composition were stacked, and two more samples were sandwiched between SUS304 plates (100 mm x 50 mm, 1 mm thick, weighing 40 g), and a 500 g weight was placed on top. - The samples were left in an oven set at 40°C for 4.5 days. - The samples were removed from the oven, the weights were removed, and the samples were left at room temperature for at least 1 hour. - The SUS304 plates were removed, and the two overlapping samples were carefully peeled off, and the state of adhesion was observed. - The state of adhesion was observed and evaluated according to the following criteria. Evaluation 1: Sticking between sample surfaces Evaluation 2: Slight sticking to the sample surfaces Evaluation 3: Slight sticking to the edge surface of the sample Evaluation 4: Minor sticking to the edge surface of the sample Evaluation 5: No sticking at all

[Shear adhesion test]
The sheets produced in the examples and comparative examples were subjected to a shear adhesive strength test in the following manner.
・Sample size: 12.5mm x 25mm
- Two SPCC substrates whose surfaces were cleaned with MEK were prepared, and the tack-free sample and a spacer having a thickness of 0.3 mm were placed on one of the SPCC substrates, and the other SPCC substrate was placed on the sample and spacer. - The distance between the two substrates was fixed using a clamp. - The sample was left in an oven set at 180°C for 30 minutes to heat it. - The clamp was removed, and a shear adhesion test was performed at a shear tensile speed of 5 mm/min.

The results of the blocking test and the shear adhesion test are shown in the table in Figure 4. Also, a photograph of the surface of the adhesive part of Comparative Example 1 is shown in Figure 3(a), and a photograph of the surface of the adhesive part of Example 1 is shown in Figure 3(b).

1... adhesive sheet, 3... substrate, 4... first layer, 6... second layer, 11, 13... adhesive portion, 12... second particles, 14... adhesive permeable layer, 22... first particles.

Claims (10)

A thermally expandable and thermosetting adhesive sheet,
A substrate;
A first layer provided on at least one surface of the substrate,
The first layer comprises:
an adhesive portion having thermally expandable first particles;
and second particles made of a different material from the first particles,
The second particles are larger than the first particles,
an adhesive sheet in which some of the second particles protrude from a surface of the adhesive portion to separate the surface of the adhesive portion from the adherend before the adhesive portion expands, and when heated, thermal expansion of the adhesive portion occurs, causing the adhesive portion to overflow from the gaps between the second particles and exposing the surface of the adhesive portion to the adherend . The adhesive sheet according to claim 1, wherein the second particles are larger than the thickness of the adhesive portion. The adhesive sheet according to claim 1 or 2, wherein the second particles have a spherical shape. The adhesive sheet according to any one of claims 1 to 3, wherein the second particles are formed from an organic material selected from the group consisting of cross-linked (meth)acrylic acid ester copolymers, cross-linked polystyrene, cross-linked urethane, cross-linked silicone, and nylon. the first layer is provided on the one surface of the base material,
A second layer is provided on the other surface of the substrate,
The second layer comprises:
The adhesive portion;
The adhesive sheet according to any one of claims 1 to 4, further comprising an adhesive permeable layer provided on a surface of the adhesive portion and allowing the adhesive composition to permeate when the first particles are thermally expanded. The adhesive sheet according to claim 5, wherein the adhesive permeable layer is formed from a material whose glass transition temperature is higher than the curing initiation temperature of the adhesive composition constituting the adhesive portion. The adhesive sheet according to claim 5 or 6, wherein the adhesive permeable layer is a nonwoven fabric. the first layer is provided on the one surface of the base material,
The adhesive sheet according to any one of claims 1 to 4, further comprising a third layer having adhesiveness at 20°C provided on the other surface of the substrate. The adhesive sheet according to any one of claims 1 to 8, wherein the particle size of the first particles is smaller than 50 μm. The adhesive sheet according to claim 1 , wherein the particle size of the second particles is greater than 10 μm.

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